Should not be too complicated, just need a relatively high-speed/high-res video capture to extract frames from and then combine them in post-processing. The trick is to carefully choose the interval between selected frames to synchronize with the bird wing-flapping rate.

I saw another article about this last year and went to try it out -- it's not that hard ... just regular video on my camera. I stacked the frames and used "Darken" mode on the layers to add the birds against the light(er) sky ...

Should not be too complicated, just need a relatively high-speed/high-res video capture to extract frames from and then combine them in post-processing. The trick is to carefully choose the interval between selected frames to synchronize with the bird wing-flapping rate.

Yep. I want to try this sometime. I can capture 4k video on the 5D Mk IV and then extract 8Mpx frames from that. Dunno how good those frames would be...